I see the error,
The problem is not your plugin Martin, the problem is the theme installed. I can fix this with a shortcode widget from this theme.
It plugin is working now.
Regards!!
Is a page set as index page (Pages secction).
In this page I create a HTML widget with it shortcode.
I’m work with a themeforest theme, named Sense and i use a HTML widget from this theme.
It’s probably the widget settings of this theme(Sense) that is not working with your plugin?
Still not working 🙁
You can see it, here: http://98.142.100.178/~renefranco/ (Test Site)
And no see error messages, only don’t show the widget correctly, only show the code.
Regards!